Aromatic polycarbonate resins have excellent transparency, heat resistance and mechanical strength and are widely used in the fields of electric appliances, machinery, automobiles, medical applications, etc. For example, they are used in optical information recording media, optical lenses and building and vehicle glazing materials.
So-called window materials such as building and vehicle glazing materials are required to have the property of blocking heat radiation from sunlight for inhibiting the elevating of temperature in rooms or cars. For the above requirement, there is proposed a resin composition obtained by incorporating hexaboride particles into an aromatic polycarbonate resin.
For example, Patent Document 1 proposes a heat radiation blocking sheet obtained from a dispersion of hexaboride fine particles in an aromatic polycarbonate resin or an acrylic resin. Patent Document 2 proposes a resin sheet obtained from a dispersion of lanthanum boride fine particles having an average particle diameter of 100 nm or less in an aromatic polycarbonate resin. Patent Document 3 proposes a resin composition obtained by incorporating boride fine particles and a low-molecular-weight compound having at least one functional group selected from a hydroxyl group and a carboxyl group into an aromatic polycarbonate resin, and a molded article thereof. Patent Document 4 proposes a resin composition obtained by incorporating boride fine particles into an aromatic polycarbonate resin having a terminal hydroxyl group concentration in the range of 100 to 1,800 ppm and a molded article thereof.
When these resin compositions are produced, generally, a melt extrusion method is employed. Specifically, a master batch containing hexaboride particles and various additives is prepared, and then, the master batch and an aromatic polycarbonate resin are melt-kneaded, to prepare a resin composition. In general, the master batch is prepared by repeating the step of mixing hexaboride particles and various additives with an aromatic polycarbonate resin a plurality of times. However, some methods of preparing the master batch have had a problem that the haze of a resin composition is increased.    (Patent Document 1) JP-A 2003-327717    (Patent Document 2) JP-A 2005-47179    (Patent Document 3) JP-A 2007-519804    (Patent Document 4) JP-A 2006-307172